1. Field of the Invention
The present invention pertains to control of a motorized flight vehicle in a medium and, more particularly, to thrust vectoring a flight vehicle during homing using a dual pulse solid rocket motor.
2. Description of the Related Art
Flight vehicles such as missiles find a wide range of very demanding applications. They are frequently employed in many different scenarios with varying degrees of lethality. These scenarios may range from non-lethal missions to the delivery of an explosive payload to disable, or even destroy, a target. Because of this potential lethality, much consideration is devoted to the design of such flight vehicles to achieve optimal performance. Optimal performance, however, can be an elusive goal. The primary reason for this reality is that the technical solutions for any one characteristic may adversely impact other performance characteristics.
Consider, for instance, speed and maneuverability. In missiles, designers favor the use of small fins, or control surfaces, because they reduce weight and drag, thereby increasing speed. Small fins, however, adversely impact maneuverability because they do not provide as much lift as larger fins. FIG. 1 illustrates a conventional approach to turning a missile 100. The missile 100, traveling on a flight path (represented by the arrow 102), activates its control surfaces (typically, one or more of the fins 104). This changes the orientation, or attitude, of the missile 100 relative to the flight path 102 in the direction of the desired flight path (represented by the arrow 106).
However, the missile 100 continues traveling in the direction of the current flight path 102 even though it is oriented toward the desired flight path 106 due to momentum. The new attitude generates lift on the fixed fins 105 that eventually forces the missile from the current flight path 102 to the desired flight path 106. Larger, heavier fins 105 increase the amount lift exerted on the missile 100. Thus, larger and heavier fins 105 produce greater maneuverability. They nevertheless increase weight and drag, thereby reducing speed. This conundrum becomes more troublesome at high altitudes where thin atmospheres hamper the ability to generate lift adequate to quickly alter the flight path of the missile 100.
In many high performance flight vehicles maneuverability is a prized performance characteristic. Such flight vehicles frequently are fired at targets that are themselves highly maneuverable. The targets, understandably, seldom wait for the flight vehicle and try to evade it. This is a much greater concern to the flight vehicle as it approaches the target because shorter distances yield shorter reaction times. Sometimes, these flight vehicles are themselves fired upon. In these situations, maneuverability may be desired to help evade the weapon fired at them. Designers frequently choose larger fins for greater maneuverability over small fins for speed in these types of flight vehicles.
One attempt to compensate for these kinds of tradeoffs experiments with motor technologies. Rocket motors may be categorized in a number of ways, e.g., by whether they employ solid fuel or liquid fuel. Traditionally, solid rocket motors burned in stages, and once per stage. Submarine-based ICBMs are classic examples of this technology. More recently, some rockets have employed what are known as “dual pulse” motors that burn twice per stage, although their practical applications are still relatively rare. The Boeing Company's AGM-69-A Short Range Attack Missile (“SRAM”) II and Lockheed Martin Corporation's Javelin shoulder launched missile systems are examples. Dual pulse motors have been found useful in improving range, alleviating thermal problems, and achieving higher end speed. Conventional uses of dual pulse motors cause other problems, however. For example, the increased high end speed exacerbates the problem of decreased reaction time.
Another approach to providing terminal maneuverability is to provide what are known as “divert motors.” Divert motors are essentially side facing thrusters. The principal consequence of the divert motors is to move the missile 100 sideways, bodily, relative to the current heading 102, as represented by the arrow 108. Divert motors are a separate system that can cause complications, such as difficulty in integrating into the control systems of the missile 100. The divert motors also add cost and weight to the missile 100, and generally decrease the reliability of the overall missile system.
The present invention is directed to resolving, or at least reducing, one or all of the problems mentioned above.